Heretofore, painting systems have been known wherein one or more spray guns or nozzles are so positioned within a spray booth as to uniformly deposit a coating on a work piece passed therethrough. Such coatings are typically of a viscous nature, comprising paint, varnish, asphaltums, vinyls, and the like. It is known that the viscosity of such coatings changes with the temperature of the coating material, such changes occurring with changes in the ambient temperature in which the spraying apparatus is maintained.
The coating material is emitted from a spray gun or nozzle under pressure. The pressure determines the flow rate of the coating from the nozzle. This flow rate is the amount of coating emitted from the nozzle in a unit of time. Presently, at the beginning of the operation of the painting system, a technician adjusts the pressure at which the coating material is emitted from the spray nozzles, such adjustment generally occurring early in the day when the coating line is set up at the beginning of a work shift. As the temperature of the plant rises through the day, the temperature of the coating similarly rises, changing the viscosity of the coating. As the viscosity of the coating changes, the flow rate from the nozzles similarly changes. In most instances, if the temperature has increased, the viscosity of the coating decreases and, for a fixed pressure, the flow rate from the nozzles increases. The result is an excessive depositing of the coating on the work piece, producing runs, splatters, or an undesirable excessive coating of the material.
Because temperature changes in the coating material are not at all uncommon, there is required a method and apparatus by which a continuous monitoring of the coating temperature may be achieved and whereby periodic adjustments of the delivery pressure of the coating may be made. The result would be a uniform desired deposit of the coating material on the work pieces irrespective of temperature changes.
The prior art known to applicant teaches various techniques for metering a film or coating onto a work piece. However, none of the art known to applicant teaches an apparatus or technique to compensate for viscosity changes by regulating the gun or nozzle pressure. Specifically, no known art teaches the regulation of nozzle pressure as a function of the coating temperature. Art known to applicant, but only of general interest, consists of U.S. Pat. Nos. 3,077,858; 3,278,843; 3,453,984; 3,527,662; 3,801,349; 4,013,038; 4,224,355; and 4,396,640.